I grabbed some rocks from my mothers plant pots yesterday poured boiling water on them from the kettle and left to soak for a while, after adding them to my snail/shrimp tank and leaving for a good 6 hours I tested the water and it was 8.8 which when I tested it the day before it was 7.4. I'm not complaining I'm just letting you all know for those who don't already because I have the same ones in my betta tank and they went through the same process.

Eep, you probably are not using a neutral rock--if you have them in with your betta I would remove them. Over time, they will raise the pH of that tank as well. Most rocks used in the aquarium are neutral and won't raise pH. Quartz, obsidian, jasper, jade, slate, granite, lava rock, petrified wood and most crystalline rocks are safe for the aquarium. Other rocks like pyrite (fool's gold), limestone, fossils, marble, sandstone, dolomite, corals and sea shells are not safe for the aquarium because they will raise your pH. Fluctuating pH is not healthy for your fish--and though the boiling almost certainly sped up the process of hardening your water, eventually without boiling, the rock is likely to leech minerals into the water.

I would remove it from the tank and get a neutral substrate from a store.

8.2 which isnt the best but its not terrible. The rock bridge thing has been in there for about a month already so I think I will just continue to test the water each week, if the PH does rise the betta will just adapt anyway.

I don't think it's a good idea. Bettas can adapt to a higher pH, but every time you change the water the pH will swing again rapidly. This constant fluctuation will put a lot of stress on the fish and might cause him to become ill. It's a real pity that you didn't pick a good rock for your project--but for the safety of the fish, I can't recommend that you keep the rocks in there. :(